Environmental cues for downstream-migrating American Eel at a hydroelectric facility

Abstract Objective The purpose of study was to identify environmental factors that influence downstream migration and passage of American Eels Anguilla rostrata in Roanoke Rapids Lake, a reservoir on the Roanoke River formed by the Roanoke Rapids Dam and Power Station. Methods Yellow- and silver-phase American Eels were outfitted with acoustic transmitters and monitored during four out-migration periods from October 2019 through March 2023 using acoustic telemetry receivers placed in Roanoke Rapids Lake and the Roanoke River downstream of the power station. The timing of downstream passage through the power station was determined using acoustic detection data. Poisson regression models were used to analyze American Eel detections in the context of environmental variables that were hypothesized to cue out-migration. Result Out-migration probability of American Eels from Roanoke Rapids Lake was influenced by time of day, rainfall, and change in lake level attributable to hydropower operations. Predictive models of out-migration probability demonstrated that the number of migrating American Eels was widely variable across environmental conditions and was particularly sensitive to changes in lake level. Conclusion The results of this study suggest that management actions, such as scheduled water releases from a dam and the consequent change in lake level (or correlated factors), can influence the onset and timing of American Eel out-migration.